Secondary recovery process



March 10, 1959 P. s. WILLIAMS SECONDARY ECOVERY PROCESS Filed May 23,1956 zmqmammm W 0 \AN v ON V. wma wzmmfiwmm 8 @263 2882 Philip S.Williams Inventor v Bywm Attorney SECONDARY RECOVERY PROCESS Philip S.Williams, Tulsa, Okla, assignor, by mesne asslgnments, to JerseyProduction Research Company Application May 23, 1956, Serial No. 586,7611 Claim. (Cl. 166-11) The present invention is broadly concerned with animproved process for increasing the recovery of crude petroleum oil fromoil bearing sub-surface formations. The invention is more particularlyconcerned with a secondary recovery operation wherein high pressuresteam is used in a particular manner to secure the recovery ofadditional quantities of oil from an oilbearing formation. In accordancewith the present process, suflicient steam pressure is used in theformation to create fissures which extend through the formation,preferably, from the injection well to a producing well or wells. Inaccordance with the technique of the present operation, a minimum amountof steam is used for a maximum production of oil and excessive losses ofheat to adjacent non-productive strata is prevented.

It has long been realized by the petroleum industry that only arelatively small proportion of the oil in a subterranean reservoir isremoved from the reservoir during the primary production stage.Specifically, it has been found that most reservoirs still generallycontain from about 40% up to as much as 85% of their original oil whenprimary production has ceased. This retention of desired oil in theproductive formation is the result of the approach of equilibriumbetween the expulsive and the retentive forces acting on the oil.Therefore, to obtain further production of oil, a change of the physicalor chemical relation between the retained oil and the formation isneeded.

Accordingly, the petroleum industry has employed a great number ofmethods or processes for secondary oil recovery. In general, thesemethods call for the introduction of a fluid within one or moreinjection Wells in a reservoir and for the subsequent withdrawal of oilfrom spaced production wells. Fluids that have been suggested oremployed for this purpose include water, flue gas, carbon dioxide,methane, propane, butane, and the like.

One of the most widely employed methods for the secondary recovery ofoil has been the waterflooding procedure in which water is injected andemployed as the driving medium. This procedure has been successful inrecovering from about to 50% of the initial oil from most reservoirs.Unfortunately, however, this waterfiooding procedure still leaves fromabout 35 to 65% of the oil in the reservoirs. Furthermore, awaterflooded reservoir is not readily adapted to other additionalsecondary recovery techniques since the water tends to decrease thetransmissibility of oil in a reservoir to an extent such that the othercommonly employed secondary recovery drive media are unable to functionproperly or efficiently.

Also, the use of steam to increase oil recovery in a secondary operationhas been proposed. However, heretofore, the method for the use of steamas a secondary recovery medium has been to use it in a manner similar toa gas or water drive wherein the oil is driven ahead of the injectedsteam as a bank of flowing oil. By this method the Water of condensationacts as a driv- .also are of relatively shallow I 2,876,838 Patented Marlt), 1959 ing medium of the oil toward producing wells and'thus furtherthe recovery of oil.

One difficulty in this method of utilizing steam is that there occurslarge, and sometimes prohibitive, heat losses to adjacentnon-oil-containing formations. These heat losses increase rapidly withtime, and thus, it is essential that the process go fairly rapidly ifthese excessive and prohibitive heat losses are to be avoided. However,the process or operation cannot be speeded up without limit, since withbank movements of fluids, it is not possible to achieve production ratesabove a certain figure due to the porosity and geological nature of theoilbearing strata. This is particularly the case in reservoirs whereinthere exist high oil viscosities and wherein the formations haverelatively low permeabilities and depths.

In accordance with the present invention, these difficulties areovercome by the use of steam of suflicient pressure so as to causefracture of the reservoir rock and to lift the overburden. When thesefractures occur, steam and condensed water will flow through the formedfissures from the injection well toward the producing Well. Under theseconditions, the temperature of the reservoir will rise rapidly as heatflows from the fissure to the surrounding oil-bearing strata bydiffusion. By operating in this manner, a limitation otherwise presentin the use of steam is removed, namely: the relatively low rate oftransfer of heat to the reservoir. By the present method of operation,any rate of heat transfer which can be supported by boiler capacity andcondensate liftingfacilities can be achieved. In operation, inaccordance With the present invention, it is not desirable that livesteam in any substantial quantity reach the producing well, since it isdesirable that the latent heat or heat of condensation of the injectedsteam be utilized to heat the oilbearing formations about the fissures.

As the steam condenses in the fissures this will tend to restrict fiowof fluid through them. This in turn will cause the steam and watertoflow through larger and larger areas adjacent the fissures, thusfurther rapidly heating up the reservoir by diffusion. Furthermore, inaccordance with the present invention, as the adjacent areas near thereservoir heat up, the pressure gradients as existing along the fissureswill begin to move oil under steam and water drive toward the producingwells. Thus, by the time the bulk of the reservoir is well heated, thesteam and condensate water will have removed substantial quantities ofoil from the reservoir. Thus, the process of utilizing steam in asecondary recovery method will be efliciently accomplished withoutprohibitive losses of heat to adjacent non-productive strata.

The process of the present invention may be more fully understood byreference to the drawing illustrating embodiments of the same.

An oil-producing formation 1 is shown positioned below the earthssurface 2. A borehole 4 and borehole 6 extend from the earths surface tothe oil production formation. These boreholes are lined with suitablecasing 20 and 21, respectively. In accordance With the presentinvention, steam under high pressure is generated in facilities 3. Thissteam is passed through injection well 4 by means of a conduit ofsufiicient strength 9. Suitable auxiliary equipment is utilized, such asa support 22, packing 23 and well head equipment 24 as well as pressurerecording gauges 25 and metering equipment 26. The high pressure steamis injected into oil-containing formation 1 in sufiicient pressure tolift the overburden 5 and to cause fissures to form in oil-containingformation 1, preferably, extending from the injection well 4 to aproducing well or wells 6. Thus, in operation, the injected highpressure steam will flow through these fissures and will besubstantially completely condensed prior to reaching producing well 6.The fluids are removed through conduit 7 in well 6 and passed tofacilities d wherein a segregation between the water and produced oil ismade.

As pointed out heretofore, the present process of creating fissures bythe use of high pressure steam overcomes the difiiculties previouslyencountered in using steam as a driving medium. Heretofore, due to theinherent nature of oil-containing formations, the drive had to proceedat a relatively low rate of production. Thus, the steam bank may haveproceeded to a particular point at which time not only was the portionof the oilproducing reservoir between the injection well and particularpoint heated, but in addition, vast areas of thenon-producing'overburden also heated. Heat is also lost to the area ofnon-oil-containing strata existing below the oil-bearing formation. Inaccordance with the present invention, the injected steam will flowthrough the produced fissures and will reach the producing well beforeheat will be lost in significant amounts to the non-oil-bearing strataexisting above and below the oilbearing formation. Whilethe presentinvention may be used with respect to any type of formation in asecondary recovery method, it is particularly adapted to fairly shallowfields. The fissuring process may tend to produce a somewhat erratic andunpredictable initial pattern of heat input fissures. Thus, it isdesirable that there exist a fairly close well spacing. Also, in orderthat lateral and vertical heat diffusion occur in a rea sonable time, itis also desirable that the flow channels enlarge themselves from theoriginal fissures in a reasonable time so as to prevent prohibitivelosses of heat to adjacent non-producing strata. Furthermore the shallowfields will require less pressure to secure the required fissures fromthe injection well .to the producing wells.

The pressure requirement for the production of fissuresin a formation,is roughly equivalent in pounds per square inch to the depth of theformation in feet. It has been found in the art of formation fracturingthis pressure, commonly referred to as the formation breakdown pressureis equal to the pressure required to overcome the rock-binding strengthand the pressure to lift the effective overburden. Due to both change inthe 4 character and the subterranean configurations of the formation,the formation breakdown pressure varies from place to place. However, asa general rule, this pressure in pounds per square inch divided by theformation depth in feet, is reasonably constant from about .6 to about.9 p. s. i. per foot of depth or to pounds per square inch per hundredfeet of depth.

This invention teaches that it is necessary to apply pressures to theformation equal to the formation breakdown pressure, a pressure which isreadily recognized. As a fluid is injected or pumped into a formation,the pressure increases until a maximum pressure is reached wherebyincreased injectionof fluid does not materially effect this pressure.This pressure is readily discernible at the well head by noting both thefluid injection rates and pressures.

While it is desirable that the fissures extend throughout the formation,this is not essential. Furthermore, the fissure pattern may change withtime. The extent and degree of fissuring necessary as well as theprecise.

fissure patternmust be of such a nature as to permit the introduction ofsufficient steam at a rate adapted to giveheat to the reservoir so thatthe operation can'be carried out before prohibitive amounts of heat arelost I to non-oil-containing adjacent strata.

What is claimed is:

In a process for the recovery of oil from a subter ranean oil formation,which ispenetrated by an injection 7 Well and a producing Well spacedfrom said injection well, including the steps of injecting steam intosaid formation through said injection well and recovering fluid from theformation through said producing well, the improvement which comprisesapplying the steam within the injection well against the formation at apressure-sufficient to fracture the formation, whereby heat is rapidlydissipated through the formation and fluid including oil and water flowsthrough said fractures to said producing well.

Yeomans Aug. 14, 1917 j Walter Feb. 14, 1956

